Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/307

Rh THELYPHON1D3.] ARACHNIDA 287 in three groups, and forming a triangle with the apex (more or less acute) directed fonvards ; the base of the triangle is formed by two lateral groups, each of three contiguous eyes ; the apex by the third group of two eyes near to gether, but not generally contiguous to each other. The falces are monodactylous, or terminating with a simple movable fang. The palpi are four-jointed, mono dactylous, or rather didactyle in a modified form. The sternum is more developed than in the scorpions, but not so fully as in the next order, Araneidea. The Idbium is either entirely wanting or very rudimentary in one family, in another fairly developed, and in another altogether absent. In any case, it is probably of small economic importance compared to the labium in the Araneidea. Such knowledge as is at present attainable in regard to the internal anatomy of this order will be noted in the sepa rate descriptions of each family. These families are three in number, Thelyphonides, Tartandes, and Phrynides, and being very distinct, it will be well to give a short diagnosis of each. Family I. Thelyphonides. EXTERNAL STRUCTUKE (tigs. 21,22). The cephalo-thorax is sometimes of a tolerably regular oval form, more or less Scale J/noTies Flo. 21. Thelyphonus yiyanteut, Koch. a. palpus; 6, movable fang or claw, form ing with f, claw on fourth joint, a didactyle claw; d, claw on third joint; /, segmcntal elongation of abdomen, supporting tail ; g, tail ; h, h, falces ; m, eyes ; o, o, first palpal joint, with characteristic denticulations. blunt-pointed before, but often it is of an oblong quadrate shape, also pointed in front, and making not only the hinder part but also the fore part somewhat angular, the latter having two obtuse lateral angles, and one acute and apical ; it is of a flattened form, and destitute of hairs and spines, but is generally granulose, and sometimes covered with more marked, but still minute, tubercles. Marks of segmental soldering are visible, as also a longitudinal groove in the medial line of the caput, similar to, but less marked than, that noted in regard to the scorpions. Beneath the cephalo-thorax are two pieces, which may be regarded as small sternal plates, perhaps the terminal remains representing the complete sternum of the Araneidea, or anticipating its complete form in that order. One of these sternal plates is of a somewhat triangular form, and is ? portion of underside, a, movable claw of palpus; 6, fixed ditto, c, claw on third palpal joint ; d, d, maxillae supporting palpi ; e,/, sternal plates; g, orifice of sexual organs; h, place of labium; 0...0, orifices of respiratory organs. has its longest or apical angle directed backwards between the basal joints of the first two pairs of legs ; the other, more heart-shaped, and with the apical angle reversed, is situated between the basal joints of the legs of the fourth pair. In some species a minute corneous patch may be seen between the coxss, or basal joints, of the third pair of legs, affording still further evidence of the remains of a sternal plate. At the centre of the fore margin of the foremost of these sternal plates is a small point which seems to represent the labium. Beneath the fore part of the cephalo-thorax are two not very powerful falces, termi nating with a long, powerful, movable, curved fang, some what resembling what we find in the Araneidea, and hinting at a transition to that order from the didactyle falces of the Scorpiones. Beneath, and opposed to, this fang is a fixed tooth-like claw ; these parts of the mouth are thickly clothed and fringed with hairs. Immediately in front of the fore sternal plate, beneath the anterior part of the cephalo-thorax, are articulated two enormous maxillos of a subtriangular form, the apex being at the articulated part, and the inner basal angle prolonged into a larger or smaller tapering, pointed apophysis, which is now and then denticulate. From the extremity of each of the maxillae springs a proportionately strong and massive four-jointed pafyus, powerfully armed with spines, denticulations, and claw-like projections ; the inner extremity of the last, or digital, joint terminates like the radial (or the joint next before it), with a strong, claw-like, sharp-pointed projection, in imperfect opposition to which there is a stronger movable claw, of the same nature, articulated to the outer extremity ; the fixed claw of the digital joint, with the joint itself, appears capable of being opposed at will to the fixed claw of the radial joint, thus giving the palpi a duplex kind of didactyle claw, didactyle, that is, in a modified sense, dif fering as it does considerably from the terminal claw of the scorpion s palpus, which is more properly spoken of as didactyle. The movable finger of this claw would, perhaps, be more correctly reckoned as a substantive joint, terminat ing with a more or less sharp corneous nail ; and this joint, opposed to a pointed apophysis of the one to which it is articulated, forms the so-called didactyle claw ; in fact, the terminal palpal claw of the Scorpiones (including the Pseudo- Scorpiones) as well as that of the Phalangidea, appears to be similarly constructed. In the present family, however, the basal portion of the joint, bearing the fixed claw, being far less developed (seldom stronger or more bulbous than the other joints), and the two fingers being always of unequal length, the didactyle nature of the whole is less real, and less apparent ; while in the scorpions its bulbous form is generally apparent, and often inordinate, the equal length of the two fingers and their evidently purposed opposition to each other making the claw, in the fullest sense, didactyle. If this view (that the movable finger of this claw is a substantive joint) be correct, the palpi in the present order, as well as in the orders Phalangidea and Scorpionidea, must be considered to have five instead of four joints, thus bringing them to an equality in this respect with the